WASHINGTON — Campaigning in economically battered Ohio this week, Hillary Clinton and Barack Obama said that as president, they'd pull the United States out of the landmark North American Free Trade Agreement if Canada and Mexico refused to incorporate core international labor rights into the treaty.

Canada and Mexico, however, already subscribe to the core standards of the International Labor Organization. Mexico has subscribed to 70 ILO conventions, and Canada has adopted 28 of them.

The United States has agreed to only 14. That's eight fewer than the number of global labor agreements accepted by China, the source of most U.S. job dislocation.

NAFTA was a major focus in Tuesday night's Democratic debate in Ohio. Clinton and Obama's underlying assertion is that jobs in manufacturing states such as Ohio, which holds a high-stakes presidential primary Tuesday, migrated to Mexico as companies took advantage of weaker worker protections there.

Ohio has lost manufacturing jobs; that isn't in dispute. But research shows that some Rust Belt manufacturing jobs went to other U.S. regions with lower costs, others were displaced by technology and automation, and, yes, some went to Mexico.

Many more, however, were lost to China and other nations that NAFTA doesn't cover. This led the U.S. Labor Department to expand NAFTA-related worker-retraining programs to more general trade-related job losses.

Mexico was among the ILO members that adopted a declaration of principles and rights for workers in 1998. These include the right of association, the right to organize and bargain collectively, the prohibition of forced or compulsory labor, the elimination of child labor and nondiscrimination in employment.

The most recent ILO report on infringement of collective-bargaining rights, issued in November, included charges against several Latin American governments but no complaints that Mexico has failed to protect workers' bargaining rights.

In its most recent survey of the Americas, in 2006, the International Confederation of Free Trade Unions had a single line about Mexico: that garment workers at times had to organize without the knowledge of their employers. The confederation devoted an entire paragraph each to union-busting activities in the United States and Canada.

In interviews with McClatchy, representatives of the Clinton and Obama campaigns couldn't cite a single labor or environmental dispute in Mexico or Canada when they argued that the two countries have shirked NAFTA or ILO commitments.

The two campaigns were virtually identical in their demand to revise the labor and environmental side agreements that were adopted with NAFTA under President Bill Clinton in 1993. Both camps want language on core ILO workers' rights enshrined in the main NAFTA treaty, as it was in the recently passed U.S.-Peru free-trade agreement.

"I think what's significant here is the concept that one is elevating labor and environment to the same status as everything else in the agreement," said Daniel Tarullo, a Georgetown University law professor who's advising the Obama campaign on trade issues.

Jaime Zabludovsky, a former top NAFTA negotiator for Mexico, warned that Obama and Clinton are sending a harmful message to a region that's been turning to left-wing politics and becoming more anti-American in recent years.

"What's much more important is the message that the U.S. is sending to the rest of Latin America: that NAFTA hasn't been a positive," he said.

President Bush noted Thursday that "there's roughly like $380 billion worth of goods that we ship to our NAFTA partners on an annual basis. Now, $380 billion worth of goods means there's a lot of farmers and businesses, large and small, who are benefiting from having a market in our neighborhood."

Canada and Mexico are the top two markets for U.S. exports. The Office of the U.S. Trade Representative lists Mexico as the top destination for U.S. exports of beef, dairy products, poultry, rice, soybean meal and oil, corn sweeteners, cotton, apples and dry edible bean exports. It's the second leading market for U.S. exports of pork, corn, soybeans, eggs and vegetable oils.

NAFTA took effect on Jan. 1, 1994, gradually reducing all trade duties. As of this year, there was one lone North American-made product still subject to duties when crossing the U.S., Canadian or Mexican borders: used vehicles.

Neither Canada nor Mexico welcomes a NAFTA revision.

"The renegotiation of NAFTA would be nothing short of opening Pandora's box. It might reinstate countless barriers to trade and rekindle the very commercial disputes that the agreement was designed to overcome, and has actually overcome," Arturo Sarukhan, Mexico's ambassador to the United States, told McClatchy.

Clinton trade adviser Larry Benn said the senator understood that America's NAFTA partners might make their own demands if the labor and environmental accords were reopened.

Canada, for example, has sought tighter controls on pollution from coal-fired power plants that are upwind in the U.S.

"We have to at least be willing to hear the other side's view if they feel that there is a shortcoming," Benn said.

A top Canadian trade official, speaking on the condition of anonymity because he wasn't authorized to discuss an internal U.S. matter, said the United States lagged behind its NAFTA partners in embracing global labor standards.

"We've (both) signed on for more core labor standards than the U.S. has. This is the biggest joke of the whole thing," the diplomat said.